Large evaporation occurs over the Sudd wetland, a huge swamp located on the Upper Nile. Historically, water resources planners have had the intention to reduce the Sudd evaporation by shortcut channels (e.g., Jonglei canal). The question is: what is the effect of draining the Sudd wetland on the regional water cycle, and on the Nile water flow? A regional
climate model has been applied to the Nile Basin, with a special modification to include routing
of the Nile flood over the Sudd. The impact of the wetland on the Nile hydroclimatology has been studied by comparing two model scenarios: the present climatology, and a drained Sudd scenario. The results indicate that draining the entire Sudd has negligible impact on the regional water cycle owing to the relatively small area covered by the wetland. The runoff gain would then be up to ~ 36 Gm3/yr. However, the impact on microclimate is large. The relative humidity will drop by 30 to 40% during the dry season, and temperature will rise by 4 to 6°C. The impact during the wet season is small.